Measuring the health of Mt. Tam

Maintaining a healthy, vibrant and diverse Mt. Tam begins with understanding how key ecological resources are faring, and how we can better care for this iconic and beloved place.

One Tam partners and Bay Area scientists have come together to try to answer the question: How healthy are Mt. Tam's natural resources?

Grasslands

Grasslands

Photo by William Follette

Why Was This Indicator Chosen?

Grassland ecosystems are dominated by both perennial and annual herbaceous plants, with little to no trees or shrubs. Dominant native grassland species in the One Tam area of focus include purple needlegrass (Stipa pulchra), blue wild rye (Elymus glaucus), clovers (Trifolium spp.), California oatgrass (Danthonia californica), and red and blue fescue (Festuca rubra and F. idahoensis), among others.

California native grasslands are among the most endangered ecosystems in the country occupying less than 1% of their historic extent (Noss & Peters, 1995). Perennial grasslands provide ample carbon storage below ground in extensive root systems (Potthoff et. al., 2005) and some species of native grasses can live for hundreds of years (Marty et al., 2005).

Nearly 90% of California’s rare plant species listed in the Inventory of Rare and Endangered Species in California (Skinner & Pavlik, 1994) may be found within California grasslands, in addition to 30% of the threatened and endangered wildlife species (over 40% of terrestrial animals) (CDFW, 2016). Badgers (Lay, 2008) and grassland-nesting birds (Rao et al., 2008) rely on large patches of grassland for reproduction and forage.

What is Healthy?

The persistence of large, intact, and native species-rich blocks, which are needed to support grassland-dependent plant and wildlife species that are sensitive to edge effects and fragmentation. Because grassland habitats have decreased dramatically in extent over the last 100 years, both statewide and on Mt. Tam, preservation or expansion of grassland acreage is desirable.

Good examples of this vegetation type can be found on Pine Mountain, in scattered patches along Highway 1, and adjacent to Bootjack Creek below Mountain Theatre.

What Are the Biggest Threats?

At nearly all grassland sites, non-native species make up the majority of the plant cover, which has caused a loss of native species diversity, changes in nutrient cycling and hydrology, and shifts in invertebrate abundances (MMWD, internal data; CNPS, 2006; Steers, 2013; Ford & Hayes, 2007)

Transition to scrublands, woodlands, and/or forest in the absence of fire, grazing, or other landscape-scale disturbance

The potential effects of climate change, including frequent drought conditions and increased evapotranspiration under warmer temperatures

Lack of episodic disturbances from fire and from grazing by antelope, tule elk, and black-tailed deer, which has resulted in the loss of native species productivity, diversity, and the loss of grasslands themselves as they convert to woody dominated communities

What is The Current Condition?

The overall condition of Mt. Tam’s grasslands is Fair. This reflects a good amount of acreage, but a cautionary condition for patch size, and significant concern about levels of non-native species invasion.

What is the Current Trend?

Overall, grasslands are Declining, primarily due to non-native plant species invasion and the associated loss of native species diversity.

Map of Grassland Loss on MMWD lands (AIS, 2008; MMWD, 2016)

How Sure Are We?

We have Low confidence in this assessment because although grasslands have been mapped on all jurisdictions, much of the available information is dated. Data on community composition and native grass species cover are also limited.